12,768 research outputs found
Nonlinear transverse cascade and sustenance of MRI-turbulence in Keplerian disks with an azimuthal magnetic field
We investigate magnetohydrodynamic turbulence driven by the magnetorotational
instability (MRI) in Keplerian disks with a nonzero net azimuthal magnetic
field using shearing box simulations. As distinct from most previous studies,
we analyze turbulence dynamics in Fourier (-) space to understand its
sustenance. The linear growth of MRI with azimuthal field has a transient
character and is anisotropic in Fourier space, leading to anisotropy of
nonlinear processes in Fourier space. As a result, the main nonlinear process
appears to be a new type of angular redistribution of modes in Fourier space --
the \emph{nonlinear transverse cascade} -- rather than usual direct/inverse
cascade. We demonstrate that the turbulence is sustained by interplay of the
linear transient growth of MRI (which is the only energy supply for the
turbulence) and the transverse cascade. These two processes operate at large
length scales, comparable to box size and the corresponding small wavenumber
area, called \emph{vital area} in Fourier space is crucial for the sustenance,
while outside the vital area direct cascade dominates. The interplay of the
linear and nonlinear processes in Fourier space is generally too intertwined
for a vivid schematization. Nevertheless, we reveal the \emph{basic subcycle}
of the sustenance that clearly shows synergy of these processes in the
self-organization of the magnetized flow system. This synergy is quite robust
and persists for the considered different aspect ratios of the simulation
boxes. The spectral characteristics of the dynamical processes in these boxes
are qualitatively similar, indicating the universality of the sustenance
mechanism of the MRI-turbulence.Comment: 32 pages, 17 figures, accepted for publication in Ap
The critical voice; A heuristic enquiry into the experience of hearing a critical inner voice to deepen our understanding of its meaning and purpose
The purpose of this thesis is to discover new ways of thinking about and understanding one’s critical inner voice. The critical voice is defined as words that are heard internally, are typically negative towards the self and others and not Auditory Verbal Hallucinations.
The research question asks if there is a meaning or purpose to the critical voice as this has often been overlooked in previous research and literature. Theories on the aetiology of the critical voice come from a Psychodynamic perspective, however by applying an Existential Philosophical perspective it is possible to widen the lens in order to discover more about it.
The chosen methodology is Heuristic which elucidates participant’s lived experience and personal meanings. Heuristics provides a richness of data by using verbatim extracts and this showcases the texture and grain of participant’s thought processes.
Seven adult women participated in this study aged between 30 and 56. The interviews were semi-structured with emphasis on talking about what was important to them. The criteria for participation were for adults over eighteen and therefore the participant’s gender and age range proved interesting.
The results yielded exciting and novel findings, which are grouped into thirteen Gathered Themes, each of which have sub themes. For example, the critical voice is ‘Not All Bad’; it can be a ‘Little Friend’; it ‘Changes Throughout Life’ and the Menopause can effect it. It was found that the Critical Voice is connected to one’s whole being and also to our external world. Of particular interest are the findings entitled ‘Safe Criticism’ where participants found ways to be critical without harm to the other.
The implications for Counselling Psychology are that the critical voice can be both a blessing and a curse; it is interconnected within oneself and to our outer world. The findings suggest that it is important to look to our own beliefs and values so that when working with clients we do not inadvertently overlook a necessary function of the client’s inner world
Nonlinear transverse cascade and two-dimensional magnetohydrodynamic subcritical turbulence in plane shear flows
We find and investigate via numerical simulations self-sustained
two-dimensional turbulence in a magnetohydrodynamic flow with a maximally
simple configuration: plane, noninflectional (with a constant shear of
velocity) and threaded by a parallel uniform background magnetic field. This
flow is spectrally stable, so the turbulence is subcritical by nature and hence
it can be energetically supported just by transient growth mechanism due to
shear flow nonnormality. This mechanism appears to be essentially anisotropic
in spectral (wavenumber) plane and operates mainly for spatial Fourier
harmonics with streamwise wavenumbers less than a ratio of flow shear to the
Alfv\'{e}n speed, (i.e., the Alfv\'{e}n frequency is lower than
the shear rate). We focused on the analysis of the character of nonlinear
processes and underlying self-sustaining scheme of the turbulence, i.e., on the
interplay between linear transient growth and nonlinear processes, in spectral
plane. Our study, being concerned with a new type of the energy-injecting
process for turbulence -- the transient growth, represents an alternative to
the main trends of MHD turbulence research. We find similarity of the nonlinear
dynamics to the related dynamics in hydrodynamic flows -- to the \emph{bypass}
concept of subcritical turbulence. The essence of the analyzed nonlinear MHD
processes appears to be a transverse redistribution of kinetic and magnetic
spectral energies in wavenumber plane [as occurs in the related hydrodynamic
flow, see Horton et al., Phys. Rev. E {\bf 81}, 066304 (2010)] and differs
fundamentally from the existing concepts of (anisotropic direct and inverse)
cascade processes in MHD shear flows.Comment: 19 pages, 7 figures, published in Phys. Rev. E 89, 043101 (2014
Contact stresses calculated for miniature slip rings
Using mathematical formulations to plot the graphs of the contact preload versus the Hertzian load, calculations of unit loading of the preloaded brushes on slip rings can be made. This optimizes the design of contact brushes and miniature slip rings
The Online Laboratory: Conducting Experiments in a Real Labor Market
Online labor markets have great potential as platforms for conducting
experiments, as they provide immediate access to a large and diverse subject
pool and allow researchers to conduct randomized controlled trials. We argue
that online experiments can be just as valid---both internally and
externally---as laboratory and field experiments, while requiring far less
money and time to design and to conduct. In this paper, we first describe the
benefits of conducting experiments in online labor markets; we then use one
such market to replicate three classic experiments and confirm their results.
We confirm that subjects (1) reverse decisions in response to how a
decision-problem is framed, (2) have pro-social preferences (value payoffs to
others positively), and (3) respond to priming by altering their choices. We
also conduct a labor supply field experiment in which we confirm that workers
have upward sloping labor supply curves. In addition to reporting these
results, we discuss the unique threats to validity in an online setting and
propose methods for coping with these threats. We also discuss the external
validity of results from online domains and explain why online results can have
external validity equal to or even better than that of traditional methods,
depending on the research question. We conclude with our views on the potential
role that online experiments can play within the social sciences, and then
recommend software development priorities and best practices
Food for Thought: Genetically Modified Seeds as De Facto Standard Essential Patents
For several years, courts have been improperly calculating damages in cases involving the unlicensed use of genetically-modified (GM) seed technology. In particular, when courts determine patent damages based on the hypothetical negotiation method, they err in exaggerating these damages to a point where no rational negotiator would agree. In response, we propose a limited affirmative defense of an implied license due to the patent’s status as a de facto standard essential patent. To be classified as a de facto standard essential patent, the farmer must prove three elements that reflect the peculiarities of GM seeds used in farming: (1) dominance, (2) impracticability, and (3) necessary to fulfill a basic need. Based on the approaches used by courts and standard setting organizations in licensing standard essential patents in technological fields such as cell phones and software, designation of some GM seeds as standard essential patents allows the courts to imply a license from patentees to farmers on reasonable and non-discriminatory (RAND) terms. Doing so shifts the case from a tort-based patent infringement suit to a breach of contract dispute and alters the damages regime from one based in compensation, deterrence, and punishment (a tort approach) to one based solely in compensation (a contractual approach). As a result of this novel proposal, the damages calculations in these suits return to economic reality
A relativistically covariant version of Bohm's quantum field theory for the scalar field
We give a relativistically covariant, wave-functional formulation of Bohm's
quantum field theory for the scalar field based on a general foliation of
space-time by space-like hypersurfaces. The wave functional, which guides the
evolution of the field, is space-time-foliation independent but the field
itself is not. Hence, in order to have a theory in which the field may be
considered a beable, some extra rule must be given to determine the foliation.
We suggest one such rule based on the eigen vectors of the energy-momentum
tensor of the field itself.Comment: 1 figure. Submitted to J Phys A. 20/05/04 replacement has additional
references and a few minor changes made for clarity. Accepted by J Phys
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